Tanks or vessels designed for the retention of fluids or liquids require fluid-tight seals and joints in order to be effective. Such tanks when of metal are found in a wide variety of applications such as, hot water heaters, water softener tanks, automotive fuel tanks, fuel storage tanks, autoclaves, and the like. The usual fluid storage vessel is circular in section and comprises a cylindrical body shell and circular end closures for the shell, the end closures being secured to the body by any conventional means, such as, welding or soldering, in the case of metal.
The use of skilled or semi-skilled manual labor to manually bond the end closures to the body of the vessel is undesirable for reasons of high labor costs and the uncertainty of the quality and consistency of the seal. In an attempt to eliminate the human element, efforts heretofore have been made to automate the bonding operation. For example, Pat. No. 2,517,853 teaches an apparatus wherein a cylindrical tank body is clamped into a frame, end closures are pressed into engagement by rotatably supported piston rods and the entire assembly is rotated about the longitudinal axis of the vessel as stationary welders automatically apply the weld seams. Pat. Nos. 2,753,826 and 2,758,367 teach somewhat simpler machines wherein cylindrical vessels are rotated by means of a stationary head stock member and a reciprocable tail stock member. Pat. No. 3,734,387 teaches a complex system including tracks, carriages and hydraulically operated frame members for positioning and rotating multiple cylindrical sections of large cylindrical storage tanks.
In each of the prior art examples mentioned the finished work product was a cylindrical vessel having a circular section and the workpiece was simply rotated about its longitudinal axis. Those devices were efficacious with cylindrical forms because the workpiece and seam to be applied moved at a constant speed and was always spaced a constant distance from the stationary welding tool. However, those skilled in the art will appreciate that the prior art devices would be ineffective with vessel structures having non-circular cross sections because of the varying speeds of rotation of the vessel surface and the spacing of the seam from the fixed welding tool.
It is, of course, well known that certain tanks are, by necessity or design, non-cylindrical in form. An example of such non-cylindrical tanks are automotive fuel tanks, and particularly the fuel tanks of highway truck tractors used for hauling trailers and the like. Typically, the fuel tanks of truck tractors are generally rectangular in section with curved or arcuate corners.
None of the known prior art devices is suitable for automated bonding or sealing methods of non-cylindrical tanks or tanks having planar surfaces and, more particularly, rectangular tanks having arcuate corners. There thus exists a need for apparatus that can rotate a tank of such form past a fixed point (viz., a welding or soldering tool, or the like) at a constant speed and with constant spacing from that point.